As shown in, for example, FIG. 20A, a method of placing a vibration reducing member 21 of a viscoelastic body such as rubber, resin and the like on a vibrating element (base member) 22 is conventionally known as a noise reduction method for construction equipment. In this method, as shown in FIG. 20B, the vibration reducing member 21 placed on the vibrating element 22 is compulsorily expanded and contracted following the movement of the vibrating element 22, which is vibrating, as shown by the arrows in FIG. 20B. Then, due to the loss determined by the physical properties inside the vibration reducing member 21 in this situation, the vibrational energy is dispersed as thermal energy, thereby producing the effect of reducing vibration.
Further, as another noise reducing method of the prior art, for example, Japanese Utility Model Laid-open No. 55-174082 discloses a shoe plate (crawler belt) of a crawler vehicle, on which underside face a vibration damping means utilizing frictional loss is attached. According to the above, one end side of the vibration damping means (for example, spring steel plate) is fixed on the underside face of the shoe plate with bolts or the like, and the other end side is attached on the shoe plate while it is firmly pressed against the shoe plate (not fixed). When the shoe plate vibrates, due to the friction caused by the displacement of the other end portion of the vibration damping means and the shoe plate, the vibrational energy of the shoe plate rapidly decreases, thereby rapidly damping the vibration.
However, the above conventional noise reducing methods have the following disadvantages.
In the noise reducing method shown in FIG. 20A and FIG. 20B, it is necessary to increase the thickness of the vibration reducing member 21 to produce a higher vibration reducing effect, and it is required that the thickness of the vibration reducing member 21 is more than twice to three times of the plate thickness of the vibrating element 22. In the case of construction equipment, since the vibrating element (base member), to which the noise reducing member is applied, has the plate thickness of more than several millimeters to ten-odd millimeters, the required plate thickness of the vibration reducing member is almost about 10 millimeters to 50 millimeters. Consequently, the vibration reducing member 21 increases in cost due to the thickness as described above, besides being originally expensive since it is made of special material. In addition, in a place where the vibration reducing member 21 is placed, it is necessary to secure a space of a predetermined size in order to avoid interference with the other members, which causes the disadvantage of the device increasing in size. Further, in the case of construction equipment and the like which are used in various sites in the outdoors, there arises the disadvantage that the attaching portion of the vibration reducing member 21 has less durability against the environment (sunlight, weather, and the like), vibration, impact and abrasion (by rocks, stones, sands and the like).
Further, in the vibration damping means described in the embodiments of the shoe plate of the aforesaid Japanese Utility Model Laid-open No. 55-174082, one end side of the spring steel plate formed into a wave-shape is pressed against the shoe plate with bolts or the like to be attached thereto. However, due to the structure in which the plate formed into a wave-shape is fixed at only one end side and pressed against the shoe plate, dirt, sands and the like easily enter the gap between the spring steel plate and the shoe plate. If these sands and the like come into the aforesaid gap, the gap is widened, thereby eliminating or decreasing the loss of vibration caused by the frictional energy, thus causing the disadvantage that the noise reduction effect does not last for a long time. Further, due to the above structure, the spring steel plate is easily deformed by stones, rocks and the like, thus causing the disadvantage of less durability.